Traveling a little over 4500 miles in the last month, Northern Ca to Louisiana and back, mostly back roads, but some time on 10 and 20, I saw no evidence of any shortage. I looked at every fuel stop, and any stores I visited that would normally carry DEF, and every one of them had stock, some with quite plentiful supplies. I did see one DEF pump at a truck stop with a note “no DEF at this time” on it on I-5 near Coalinga. I dont buy bulk DEF for my coach, but I didn't notice this elsewhere and probably would have.
What I did see however were insanely high prices in Texas for box DEF - around $20 and as high as $26 for one 2.5gal jug. When I asked about it the clerks all stated they had no idea why the price went up. My guess is that while there may be plenty of DEF to go around store owners are relying on rumors of a shortage to justify the price increase. At home I pay around $12/2.5 gal for box DEF and this is still the going rate here.